Observation of self-bending and focused ultrasound beams in the megahertz range

Self-bending (or self-accelerating) and nondiffracting acoustic beams, such as Airy beams, have the potential to focus around obstacles that are directly in the beam path. Here, we demonstrate the self-bending and focusing properties of Airy beams in the ultrasound domain using finite difference time-domain simulations at 5.2 MHz. The phase profiles of self-bending Airy beams are determined from the Airy function. This beam is then transmitted experimentally using a linear array transducer connected to a 128 channel Vantage Verasonics operating at 5.2 MHz. The performance of self-bending beams is compared to conventional focused ultrasound beams in the presence of a strong scattering obstacle (steel rod). The ability of self-bending Airy beams to bypass obstacles is characterized in terms of their relative energy retention at peak intensity, that was found experimentally to be 50.5% for traditional focused beams whereas 71.5% for Airy beams, proving that self-bending beams performed better than conventional beams in terms of relative energy retention with no significant change in the focal profiles. However, it is observed that, in absolute terms, self-bending beams focus less energy than traditional focused beams.